LED power driver RMS value measurement and resolution

- Jan 31, 2018-

It is well known that the quality of LED lighting products depends on two aspects: one is the LED chip source; the other is the LED power driver. At present, to provide high-quality qualified LED chip is mainly a few well-known international companies such as PHILIP, OSRAM and CREE and a few other manufacturers. In general, there are few major LED chip quality problems, poor quality of the market now LED lighting products a large part of the drive power. In view of the importance of LED drive power, this article mainly discusses LED drive power measurement and measurement of some of the common technical description.

There are several prerequisite test items for LED driving power measurement such as crest factor, effective power, reactive power, apparent power, power factor, voltage / current (Valid values Valid values of RMS) and THD harmonic parameters. In the actual measurement process, many people find that they test data obtained on the test equipment and their use of power meters or multimeter data are quite different, which is more controversial reflected in the voltage / current RMS, apparent Power, Power Factor, RMS rms, and average. Many customers report that they have their own voltage / power supply (RMS value) measured with a watthour meter or a multimeter, and those less than or greater than those found on the drive test equipment. Here are some examples to show that all the data displayed on the drive tester Is the true rms value of RMS. Usually, we say the average current is also the average value of RMS. The average current is only the average RMS current during start-up test. The software data is consistent with the instrument data. At the same time according to the international standard test drive power is to test RMS real RMS; test average is meaningless. Drive the voltage, current and power displayed on the tester, but the voltage multiplied by the current is not the power; the value obtained by multiplying the current by the direct voltage is the apparent power, and the driving tester measures the active power. If you just test the average, then the test equipment does not make any sense, with a simple multimeter can test the value. According to the IEC standard, the voltage RMS, Irms, active power (P) and power factor (PF) are calculated as follows:


In the above formula, N is the number of sampling points in the cycle (the cycle depends on the frequency of the signal under test) and the value of a sampling moment. The instrument provides two methods to calculate the total harmonic distortion (THD), namely IEC and CSA, respectively:


In the above two formulas:

THD: Indicates the relative value of total harmonic distortion of voltage or current

C: K-th harmonic RMS voltage or current

K: harmonic frequency

N: the maximum harmonic frequency (the instrument is 50)

C: Effective value of the fundamental (ie, 1st harmonic) voltage or current.

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